This invention relates to binder compositions for foundry sand molds and cores which are used for nobake process or cold box process in which curing is done by contact with an amine-containing gas.
In foundry industries, binder compositions for foundry sands are very useful for making sand molds and cores.
The binders which have been hitherto used for making foundry sand molds and cores include inorganic and organic binders, which have both merits and demerits. Fully satisfactory binders have so far not been found.
The method for making foundry sand molds and cores with inorganic binders is represented by the method which comprises making sand molds and cores from the sand on which water glass has been deposited and then passing carbon dioxide therethrough to set the molds.
This method, however, has poor shakeout characteristic of cores when castings are taken out after pouring molten iron or aluminum into the sand molds to form the castings, which results in lower production speed.
Other problems encountered in the method are that the foundry sands cannot be reused, that the used sands cannot be readily disposed of because of environmental alkali pollution, that it is difficult to obtain castings having beautiful casting surface because of defects due to gas during casting, and others.
The method for making foundry sand molds and cores with organic binders is represented by the method using furan resins or phenolic resins.
When the sand molds and cores are made by curing furan resin or resol-type phenolic resin with a strong acid such as paratoluene sulfonic acid or phosphoric acid, the curing velocity fluctuates markedly with the ambient temperature.
The method for setting sand molds and cores by the reaction of phenolic resins with organic isocyanate compounds is also used widely as the Ashland method (e.g., U.S. Pat. Nos. 3,409,579; 3,676,392; 3,702,316 and 3,726,867). As far as I am aware, however, the shakeout characteristic of the foundry sand cores in this method is also not satisfactory when castings are taken out of the sand or metal molds. Especially when castings have complicated core configurations such as cylinder heads and intake manifolds are made from light alloy materials, the post-treatment step of stripping off core sands requires much labor since the core sands do not easily come out. Also in the shell-mold method wherein sand coated with novolak-type phenolic resin and hexamethylene tetramine is thermo-set, the shakeout characteristic of sand cores is poor. Especially in the case of aluminum castings, the castings are often heat-treated (500.degree. C..times.1 to 4 hours) in an oven to strip off the core sand.